1. Field of the Invention
The present invention relates to an optical photographing system, and more particularly, to a compact optical photographing system used in an electronic product.
2. Description of the Prior Art
The demand for compact imaging lens assembly has grown in recent years as the popularity of portable electronic products with the photographing function has increased, and the sensor of a general photographing camera is none other than CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor Sensor). Furthermore, as advanced semiconductor manufacturing technology has allowed the pixel size of sensors to be reduced, and the current electronic products are with the trend of good function and compact appearance, there is an increasing demand for compact imaging lens assembly featuring better image quality.
A conventional high-resolution imaging lens assembly generally adopts a front aperture stop and four lens elements, wherein the first and second lens elements are mostly spherical glass lenses which are adhered together to form a doublet for correcting the chromatic aberration. The lens assembly disclosed in U.S. Pat. No. 7,365,920 serves as one such example. However, this kind of arrangement has the following disadvantages. First, the degree of freedom in arranging the lens system is curtailed due to the employment of excess number of spherical glass lenses; thus, the total track length of the system cannot be reduced easily. Second, the process of adhering glass lenses together is complicated, posing difficulties in manufacture. Moreover, as the size of imaging lens assembly are becoming smaller, assembling lens elements compactly within a limited space tend to cause unnecessary light rays to reflect too many times within a lens barrel, which will affect image quality. Thus, to improve image quality, the unnecessary light rays should be prevented from entering the image forming area.
In the light of foregoing, a need exists in the art for an optical photographing system that features better image quality, maintains a moderate total track length and is applicable to compact portable electronic products.